Interactive effects of CO2 concentration elevation and nitrogen fertilization on water and nitrogen use efficiency of tomato grown under reduced irrigation regimes

The interactive effects of CO2 concentration elevation, N fertilization, and reduced irrigation regimes on water and nitrogen use efficiency (WUE and NUE) of tomato (Solanum lycopersicum L.) plants at both leaf and whole plant scales were investigated in a split-root pot experiment. The plants were grown in two separate climate-controlled greenhouse cells at atmospheric [CO2] of 400 (a[CO2]) and 800 (e[CO2]) ppm, respectively. In each cell, plants were fertilized at either 1.5 or 3 g N per pot. The leaf physiological parameters, C and N content in stem, leaf and fruit were determined, and both WUE and NUE were evaluated. Plants harvested from 3 g N per pot associated with e[CO2] environment possessed the greatest photosynthetic rate (Pn) and lowest stomatal conductance (gs) and transpiration rate (Tr), resulting in the highest WUE at stomatal and leaf levels. Especially alternate partial root-zone irrigation (PRI) strategy coupled with e[CO2] had the potential to synergistically reduce gs and Tr while sustain Pn and leaf water status, and further improve tomato leaf WUE. e[CO2] combined with sufficient N fertilization enhanced the biomass, C accumulation and N uptake of plants under reduced irrigation; yet the WUE and NUE at whole plant scale were affected solely by the N supply being greater in low N fertilizer. These findings provide useful knowledge on efficient irrigation and N management for adapting to the future water-limited and CO2-enriched environment.